The present invention relates to fasteners in general, and, more in particular to engine clip bolts.
Engine clip bolts fasten parts of aircraft engines together. Clip bolts are used where the head of the bolts cannot be held during installation and removal. Clip bolts do not rotate during installation and removal of cooperating nuts. Clip bolts also are constrained axially before nut installation and after nut removal. With clip bolts, parts of an engine can be properly registered with respect to each other and the parts moved and rotated without the nuts being installed.
To prevent rotation of a clip bolt, its clip bears against structure of the engine. More specifically, each clip has an ear attached directly to its bolt and that extends laterally away from the bolt to a tang or hook that bends back towards the bolt. The bight of the hook mechanically interferes with the structure of the engine to keep the clip bolt from rotating during nut installation and removal. The nose of the hook axially interfers with the structure to keep the clip bolt with the engine structure even without the cooperating nut.
The clip should be reliably and strongly attached to its bolt. If the clip and the bolt come rotationally unattached during installation and before the desired amount of tightening, the nut cannot be further tightened on the bolt, resulting in an unsatisfactory joint. Clips of the clip bolts cannot separate from the structure they are used with because of the danger that the clips will be ingested into the engine. To avoid the possibility of separation, the bolts use clips that stay with the bolt even if they become rotationally uncoupled.
Attaching the clip to the bolt presents problems. Welding the clip to the bolt can affect the metallurgy of both, and the reliability of the resulting joint is not always good. Welding is also an expensive procedure. Another approach uses axially extending pins of the bolt that receive the clip and that are swaged to lock the clip to the bolt. Problems with this approach include expense and a high percentage of unreliable unions. A third approach uses an externally splined bolt that receives internal splines of the clip with the end of the bolt again swaged over the top of the clip to axially lock the two together. This third approach is also expensive because of the external splines on the bolt and because of the necessity to register the external and internal splines during assembly.